Multiple Structure Cathodic Protection System

ABSTRACT

The invention is a multiple-structure cathodic protective system that includes multiple voltage-controlled outputs to protect multiple structures with a common ground bed, or a single structure with multiple anode ground beds. Each output feeds an individual cable that is powered by independent pulse-width-modulated voltage power supplies. Current through the cables is monitored and the PWM control compensates to maintain the correct amount of current for maximum protection and long life.

CROSS-REFERENCES TO RELATED APPLICATIONS

None.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

None.

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

None.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

None.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to cathodic protection of buried metal structures using continuous electric current from a single voltage source.

2. Background Art

Buried metal structures corrode due to voltage differences between the ground and the various different contact points of the structure. Because of the voltage difference, a continuous current develops in the structure that causes hydrogen to form in the cathodic points of contact, and iron corrosion in the anodic points of contact.

Eventually, the electron flow will corrode enough iron to weaken a buried structure and develop leaks or failures. The term “cathodic protection” refers to the practice of using current through the structure to combat the corrosion by artificially forcing the structure to be at a negative voltage in comparison to the surrounding ground connecting the negative terminal of a direct current voltage source to the structure and connecting the positive terminal to a sacrificial anode buried near the structure. The term “sacrificial anode” comes from the use of the anode—it is slowly eaten away as it provides a steady stream of ions to provide the cathodic protection.

When the applied voltage is correctly set, the electrons flow from the anode to the structure, and the structure does not corrode. The current flow must be set so that the structure remains cathodic (draws electrons to the structure from the surrounding ground), but not so cathodic that the electron flow is excessive, which causes the structure to become weak and brittle.

The cathodic protection industry struggles with development of a system to protect multiple structures, as each structure exists in a slightly different resistive ground network. A single voltage source results in different current flow to each structure. The various approaches include the insertion of variable resistors along the cable network to even out the current (Al-Mahrous, U.S. Pat. No. 7,192,513), use of multiple buried anodes of different values of resistance that provide different amounts of protection, and use of multiple anodes that are switched off and on to provide more or less resistance (Husock U.S. Pat. No. 3,143,670).

As these patents and the product offering of the cathodic industry demonstrates, the search for efficient protection of buried metal structures has been a fifty-plus year endeavor that continues to this day. Those in the industry must weigh many factors to select a proper product. Those factors include system hardware cost, system operational cost, system reliability, energy efficiency, and number and size of structures to be protected. There is no one-size-fits-all solution, as a pipeline with easy access to electric utilities will naturally call for a different solution than a single well in an isolated area.

BRIEF SUMMARY OF THE INVENTION

The invention is a multiple-structure cathodic protective system that includes multiple voltage-controlled outputs to protect multiple structures with a common ground bed, or a single structure with multiple ground beds. Each output feeds an individual cable that is powered by pulse-width-modulated voltage power supplies. Current through the cables is monitored and the PWM control compensates to maintain the correct amount of current for maximum protection and long life.

In the current embodiment, a computerized control system monitors the current and voltage drop across each protected structure circuit, adjusting the current through each line corresponding to the drop by adjusting the voltage output. In this way, the system gives protection with a single bulk power supply and multiple power supply outlets, reducing cost while maintaining a flexible configuration that other single-source cathodic protection systems do not possess.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1—A schematic diagram of the invention configured to protect multiple structures using a common anode bed.

FIG. 2—A schematic diagram of the invention configured to protect a single structure using multiple anode beds.

FIG. 3—An operational flowchart of the invention configured to protect multiple structures.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows one embodiment of a computerized voltage-controlled multiple-output cathodic protection unit 11 that could be used to inhibit corrosion in buried metal structures. The cathodic protection unit 11 includes: a main computer 13, said computer comprising an input power converter 17, and one or more power supply output cards 31, 33, 35 (hereafter “31”) which fit into the main computer 13, and each power supply card 31 providing a pulse-width-modulated voltage supply output at the card terminals. An optional user-interface 41 can be used to provide input to the system to make changes, read results, or report alarms. The positive terminals are tied to a sacrificial anode 19, and the negative terminals of each output card 31 are tied through respective cables 21, 23, 25 to individual metal structures to be protected, shown as impedances Z1, Z2 and Z3. In this embodiment, each card has its own output circuit that protects a single structure.

In the embodiment shown in FIG. 1, the input power supply converter 17 accepts the available external power supply at input terminals 15 and converts it to an intermediate bus voltage. Depending upon the specific installation, the input power supply converter 17 is constructed to accept such typical supplies such as 120 Vac, 240 Vac, and 480 Vac. The input power supply converter 17 provides an intermediate bus or multiple buses of voltage levels convenient for the main computer 13 and as input power to the power supply cards 31.

Each power supply card 31 converts power from the input power supply 17 to a voltage level calculated by the cards to deliver optimal current flow through a particular protected device by traveling through a common buried anode 19, through the soil to a particular protected structure, and then a cable back to the cathodic protection unit 11.

The system can be configured to operate in accordance with software programming permanently installed in the computer 13 such that no user interface is necessary, or be configured to accept user input during operation by an optional user interface 41. The user interface 41 also represents the ability of the system to report operating conditions, including the voltage and current output of each output power supply card 31, as well as any alarm conditions indicating a need for concern, such as an increase amount of current draw across a structure. Such reporting can be by digital output to a distant computer, a visual or audible alarm, or any other type of signal to operators using other currently available monitoring devices not discussed here. (In the current embodiment, output voltage of 2V or less causes an alarm.)

In most electrical circuits, a power source is set to provide a set voltage for a set load. In cathodic protection systems, changing soil and moisture conditions can radically impact the load impedance, potentially causing a set voltage to deliver too little current to protect the structure, or too much current which embrittles the metal structure being protected. To counter this, the current through each return cable is monitored by an internal current meter contained within each power supply card 31 and each card independently adjusts its output voltage in real time to maintain an optimal constant current at an operator-preset level. Cathodic protection systems vary considerably on the optimal current, from a few milliamps to 15A in some larger systems. The current embodiment can deliver 15A to a multitude of outputs.

FIG. 2 shows another possible embodiment, similar to the first described configuration, except that the system is employed to protect a single buried structure using multiple anode beds. To protect a single structure, the negative terminal of the output power cards 31 are connected to the structure to be protected, represented in FIG. 2 as Z4, and the positive terminals are connected to different buried sacrificial anodes 51, 53 and 55, typically spread out around the structure to be protected. This configuration efficiently protects a larger structure by providing multiple sources of current flow.

FIG. 3 is a flowchart, showing the step-by-step operation of one embodiment of the invention. This flowchart assumes that a user has energized the system provides either AC or DC power to power input terminal 15, and removal of power to the input terminals ceases operation of the invention. One rendition of the operational steps includes:

-   101) A user begins operation of the cathodic protection by some     action, such as pressing a button or turning a knob, or changing     position of a switch from an “off” position to an “on” position. The     switch or control can be located physically on the invention or at a     hard-wired control panel located distant from the invention. At any     time, an operator can cease cathodic protection by changing the     position of the switch or other control back to its “off” position. -   102) Once energized and in operation, the main computer 13 provides     instructions and receives feedback from the output cards 31     regarding current and voltage conditions, including any alarm     conditions, reporting those conditions to any optional     user-interface 41. -   103) The main computer initially instructs the output cards 31 to     provide an initially minimal voltage to its output terminals. The     output cards determine the current through their respective     terminals with an internal meter. The current through the terminals     is compared to a target protective current set-point. If the     terminal current is below the optimal current set-point, the card's     output voltage is raised until the terminal current is within an     operator-set acceptable range of the optimal set-point, OR a maximum     allowable output voltage is reached. -   104) If the terminal current is within the acceptable range of the     optimal set-point, the voltage output card continues monitoring the     voltage and current until the current through the terminals climbs     above or below the acceptable range. -   105) Optionally, if an unacceptably high level of current continues     to flow through an output card without a current, or an acceptable     current cannot be maintained for lack of sufficient input voltage,     the computer 13 or card 31 sends an alarm to the user-interface. -   106) Optionally, after sending indication of an alarm, shut down the     system until the operator resets the system.

While this invention has been described as it is currently built, the invention is not limited to the disclosed embodiments, but can be employed in various equivalent arrangements included within the spirit and scope of the claims. In particular, the change in configuration between protection of one multiple structures and one anode bed to a single structure protected using multiple anode beds is easily understood given the explanation provided to any person having ordinary skill in the art, as well as a configuration in which multiple structures are protected with multiple anode beds, though this configuration is not shown.

Among the possible variants, the invention can be simplified such that the main computer need not exist. In this embodiment, the input power converter 17 provides an intermediate bus voltage that each output power supply converts to maintain a current setting that is hard-wired into the card, or set by a physical control on the card. Similarly, a more exotic embodiment might include computer control to create a rotating duty of output cards to reduce energy consumption or detect circuit flow interaction.

The explanation contained throughout this specification discusses three-output units merely for discussion purposes. The invention is not limited to three outputs, but anticipates as many outputs as the input power can supply sufficient current to protect the target structures. In the current embodiment, four outputs and more are typical. 

1) A computerized voltage-controlled multiple-output cathodic protection unit 11 used to inhibit corrosion in multiple metal structures, comprising a main computer 13, said computer comprising an input power converter 17, one or more output power supply cards 31, 33, 35 which fit into the main computer 13, and each power supply card providing constant current to respective metal structure Z1, Z2, Z3 through common anode bed
 19. 2) A computerized voltage-controlled multiple-output cathodic protection unit 11 used to inhibit corrosion in a metal structure Z4, comprising a main computer 13, said computer comprising an input power converter 17, one or more output power supply cards 31, 33, 35 which fit into the main computer 13, and each power supply card providing constant current to a metal structure Z4 through multiple anode beds 51, 53,
 55. 3) A method of protecting multiple metal structures from corrosion by a) converting an input power source 17 to one or more DC voltage buses suitable for powering a computer 13 and one or more power supplies 31 of at least 30 W; b) powering one or more independent power supplies 31 from the DC voltages 17, c) connecting each of the positive terminals of the independent power supplies to a buried anode bed, and d) connecting each negative terminal of the independent power supplies to a respective metal structure to be protected; and e) adjusting the output voltage of the independent power supply so an optimal current flows through the structure to be protected. 4) A method of protecting a single metal structure from corrosion by a) converting an input power source to one or more DC voltage buses with an input power converter 17, the outputs suitable for powering a computer and one or more power supplies 31 of at least 30 W; b) powering one or more independent power supplies 31 from the DC voltages, c) connecting each positive terminal of the independent power supplies to an independently located buried anode bed 51, 53, 55, and d) connecting each negative terminal of the independent power supplies to a metal structure to be protected Z4; e) adjusting the output voltage of the independent power supplies 31 so an optimal current flows through the return line from the structure to be protected. 5) A method as in claim 3, with the additional steps of: a) providing an alarm when a short has developed such that current above a user-set level is flowing through an independent power supply; and b) shutting down the outputs of one or more independent power supplies when an alarm sounds, and then after a preset amount of time or an operator reset of the system; c) returning each power supply to service. 6) A method as in claim 4, with the additional steps of: a) providing an alarm when a short has developed such that current above a user-set level is flowing through an independent power supply; and b) shutting down the outputs of one or more independent power supplies when an alarm sounds, and then after a preset amount of time or an operator reset of the system; c) returning each power supply to service. 